Gases, such as oxygen, nitrogen and argon, are delivered to a use point in a number of ways. When the use of such gases requires relatively small quantity of gas at one time, such as in metal cutting, welding, blanketing or metal fabrication operations, the gas typically is delivered to the use point and stored there in a gas storage cylinder.
A recent very significant advancement in the field of such gas storage vessels, such as gas cylinders, is the high strength cylinder described and claimed in U.S. Pat. Nos. 4,461,657 and 4,578,113, the disclosures of which are incorporated herein by reference. This new gas storage cylinder enables the storage and transport of significantly more gas than is possible in a conventional cylinder of comparable size and weight because the gas can be safely maintained within the new gas storage cylinder at a pressure much higher than that possible with such conventional cylinders. For example, whereas a conventional cylinder may safely hold gas at a pressure up to about 2700 psia, the new high pressure gas storage cylinder may safely hold gas at a pressure up to about 4500 psia.
Gas is used at a use point at a defined pressure or pressure range. Generally, this use pressure is less than the pressure of the gas source and typically is around 50 psig. In such cases, a pressure regulator is employed to cause a reduction in the gas pressure and to ensure that the pressure of the gas going to the use point does not exceed the allowable use point pressure limit. The new gas storage cylinder provides gas at a pressure significantly in excess of the conventional pressures and thus at a pressure greater than that which can be handled by conventional regulators.
Once the new high strength gas storage cylinder is empty of gas, it must be refilled. In order to retain the advantages of the high strength cylinder, it must be recharged at the high pressure. In U.S. Pat. No. 4,844,111, the disclosure of which is incorporated herein by reference, there is a described a regulator which is capable both of rendering a high pressure gas source compatible with a lower pressure use point and also enabling recharging of the high pressure gas source to a high pressure. For this purpose, the regulator is equipped with two outlet ports, one to be used by the user to withdraw gas and the other to be used for refill.
One of the problems associated with the new high strength gas cylinders equipped with this regulator is the lack of a contents gauge on the gas cylinder. This lack of a contents gauge is problematical to users of the cylinders, particularly with respect to mobile operations, where an operator desires to know how much gas is in the cylinder, so that he can ensure that sufficient gas is available for the expected activity.